In recent years, there has been a global initiative to reduce traffic noise and improve comfort in automotive vehicles. Engineers have to meet stringent government regulations while still improving the passengers’ experience. One requirement involves a measurement procedure commonly referred to as Pass-by Noise. The maximum allowed sound level for Pass-by Noise has recently been reduced, now representing a new constraint on the design of commercial vehicles. Countermeasures to reduce noise emissions consist in moderating the different acoustic sources by either acting on the noise generating mechanisms or managing the noise propagation. Adding sound absorbing materials or modifying parts of the vehicle geometry are solutions that engineers are investigating to solve this problem. With its wide range of vehicles, the Renault team has to anticipate the evolution of Pass-by noise regulations and design vehicles according to future constraints. Renault decided to extend its acoustic simulation capabilities and model the exterior acoustic propagation using Actran, a product of FFT, an MSC Software Company. With Actran, Renault was able to improve their designs and reduce development costs by considering the vehicle acoustics early in the design phase.
When studying Pass-by noise, it is essential to make sure that the numerical simulation is accurate. The absolute sound level recorded during the test determines if the vehicle will pass or if it will be rejected. “We had some measurements from physical testing available when we started the validation,” Philippe explains.
“When we started the project we were quite far, we needed to analyze the results and understand the problems in the way we were modelling. Now we are quite happy with the results. We went quite fast in improving the accuracy.” Following this successful validation phase, the methodology is now used daily by Renault engineers to optimize the technical definition of the vehicle to be sure that absorbing materials will be placed exactly where needed. “Compared to the initial target, we achieved much better performances. We started from scratch for this exterior acoustic problem, and what we were able to achieve in just a couple of years in this project is quite impressive to me” concludes Philippe.
Reducing development costs by integrating acoustic constraints at early stages through simulation.